Field of the Invention
The present invention relates to a light source unit having an optical device having a diffusing layer and a dichroic layer, a projector, the optical device and an optical device manufacturing method.
Description of the Related Art
In these days, data projectors are used on many occasions as an image projection system which projects an image of a screen of a personal computer or a video image, as well as images based on image data which is stored on a memory card on to a screen. In these data projectors, light emitted from a light source is collected to a micromirror display device called a DMD (Digital micromirror Device) or a liquid crystal panel for display a color image on a screen.
Conventionally, the mainstream of these data projectors has been those which utilize a high-intensity discharge lamp as a light source. In recent years, however, there have been developed or proposed projectors that use as a light source a light emitting diode, a laser diode, an organic EL (electroluminescence) or a luminescent material. For example, the Japanese Unexamined Patent Publication No. 2011-154168 (JP-A-2011-154168) discloses a projector having a red light source device in which a red light emitting diode emits light in the red wavelength range, a green light source device in which a luminescent material layer laid out on a luminescent wheel emits light in the green wavelength range by light emitted from an excitation light source being shone on to the luminescent wheel, and a blue light source device which is made up of a blue light emitting diode.
Then, a dichroic mirror is disposed in a position where the axes of light emitted from the excitation light source and light emitted from the luminescent wheel intersect the axis of light emitted from the red light source device, and a dichroic mirror is also disposed in a position where the axis of light emitted from the red light source device intersects the axis of light emitted from the blue light source device. The dichroic mirror disposed in the position where the axis of light emitted from the excitation light source intersects the axis of light emitted from the red light source device transmits light in the red wavelength rage and light in the blue wavelength range which is emitted from the excitation light source and reflects light in the green wavelength range. In addition, the dichroic mirror disposed in the position where the axis of light emitted from the red light source device intersects the axis of light emitted from the blue light source device reflects light in the red wavelength range and light in the green wavelength range and transmits light in the blue wavelength range. Thus, these dichroic mirrors allow the light emitted from the excitation light source to be shone on to the luminescent wheel and the light in the red wavelength range emitted from the red light source device, the light in the green wavelength range which is the light emitted from the luminescent wheel and the light in the blue wavelength range emitted from the blue light source device to be shone on to a display device via a light guiding optical system.
In the projector disclosed in JP-A-2-11-154168, since light emitted from the blue laser light emitting device is shone directly on the luminescent material layer of the luminescent wheel without being diffused, there fears that burning is generated in the luminescent material layer, and it also becomes difficult to extend the life of the luminescent material layer.
As to light in the red wavelength range and light in the blue wavelength range which are emitted from the LEDs which are solid light emitting devices, unevenness in luminance may be generated in projected light, which is projected on a screen, leading to difficulty in enhancing the quality of a projected image.
Consequently, an object of the invention is to provide a light source unit which can ensure the degree of freedom in layout in an interior thereof while protecting a luminescent material layer of a luminescent wheel, a projector using the light source unit, an optical device making up the light source unit, and an optical device manufacturing method.